I am likely going to use the FineMolds ring as it looks like it will adequately lessen the pitch along the top of the cowl but I'm going to turn one up to a slightly greater diameter to see which might be the best option.
I purchased a piece of 1" dia polystyrene rod from McMaster-Carr . They are an amazing organization- probably hundreds of thousands of items in inventory- tools, supplies, raw materials-pretty much everything in industrial supply. Easy to use website, excellent service- I usually receive my order the following day- and they have never been out of stock on anything I have ever ordered.
I next filed up two profile cutters out of a piece of mild steel bar stock- one for the radius on the outside and another for the profile on the inside-
The rod was then chucked up in the three jaw chuck- once machining has begun it cannot be disturbed or subsequent operations may not be concentric so you must be certain that you have enough working room for the tooling yet have the minimum mount of stock protruding as it will not be supported by the tail stock in this type of work.
I hoped to place an image of the rod chucked in the lathe here but the gremlins have returned . Here then are the order of operations and hopefully the pics will follow.
1. Facing- cutting across perpendicular to the axis of rotation
2. Light turning- truing up the diameter
3. Center drilling - starting a hole in the end of the stock
4. Boring- enlarging the hole in the stock to the diameter of the opening in
the cowl ring - essentially turning from the inside
5. Turning- reducing the outside to the required diameter
6. Profiling - creating the radius on the outside
7. Profiling- creating the profile on the inside
8. Parting- cutting off the workpiece from the stock
I guess I'm lucky the gremlins let me get this far- I'll try again later with some more pics.
Thanks for looking - Richard